1. Field
The present invention relates to a continuous method for synthesizing a diene elastomer that is modified by an alkoxysilane group.
2. Description of Related Art
Now that savings in fuel and the need to protect the environment have become a priority, it is desirable to produce polymers having good mechanical properties and a hysteresis that is as low as possible in order to be able to process them in the form of rubber compositions that can be used for the manufacture of various semi-finished products that are incorporated in the composition of tires. In order to achieve the objective of the drop in hysteresis, many solutions have already been tested. In particular, mention may be made of the modification of the structure of the diene polymers and copolymers at the end of the polymerization using functionalizing agents for the purpose of obtaining a good interaction between the polymer thus modified and the filler, whether this is carbon black or a reinforcing inorganic filler. It has in particular been proposed to use diene polymers functionalized by alkoxysilane derivatives. By way of illustration of this prior art relative to reinforcing inorganic fillers, mention may for example be made of U.S. Pat. No. 5,066,721 and patent application EP A 0 299 074.
It has also been proposed to combine functionalization by amine functions with functionalization by alkoxysilane functions. By way of illustration of this prior art, mention may for example be made of patent EP 0 992 537 which describes an extended elastomer that is modified at the chain end by an alkoxysilane function and that bears, at the other end or along its chain, one or more amine functions.
Furthermore, elastomers have also been proposed that are functionalized at the chain end by alkoxysilane functions bearing an amine group. Mention may be made, for example, of patent application US 2005/0203251 which describes an elastomer functionalized at the chain end by an alkoxysilane bearing an amine group.
The applicant companies have described, in document WO 2009/133068 A1, a functionalized diene elastomer essentially consisting of the species coupled by an elastomer having within the chain a group bearing an alkoxysilane function and an amine function, the silicon atom of this group bonding the two parts of the diene elastomer chain. This functionalized elastomer gives the composition containing it improved mechanical and dynamic properties, especially an improved hysteresis while maintaining a satisfactory processability in the uncured state, with a view in particular to use as a tire tread.
For those who develop materials intended for the manufacture of tires, improving the compromise of mechanical and dynamic properties of the rubber compositions, with a view to improving the performance of the tire containing them, is a constant preoccupation. This concern for improving the compromise of properties must, in so far as possible, come under an approach that aims to minimize the impact on the aspects further upstream which are, for example, the synthesis of the components of rubber compositions and their specific characteristics.
In U.S. Pat. No. 7,807,747 B2, it has been proposed to improve in particular the processability of a functionalized elastomer by using a single functionalizing agent, an alkoxysilane compound bearing an amine function, by targeting a specific distribution of the species within the elastomer. The strategy consists in adding the amine-containing alkoxysilane compound, preferably amine-containing trialkoxysilane compound, in two steps during the functionalizing step: i) first addition in an amount such that the n(amine-containing trialkoxysilane)/n(butyl lithium) molar ratio is between 0.05 and 0.35, ii) then second addition in an amount such that the final n(amine-containing trialkoxysilane)/n(butyl lithium) molar ratio is greater than or equal to 0.5. This process makes it possible to obtain a functional diene elastomer mixture comprising 40 to 80% by weight of chain-end functionalized elastomer, 5 to 45% by weight of elastomer functionalized in the middle of the chain and 3 to 30% by weight of star-shaped elastomer. The functionalized elastomer is synthesized according to a batch process.
The modification of the elastomers is an important means for improving the properties of the rubber compositions containing them with a view to improving the performance of the tire containing them. Yet it is observed that in the past the processes for modifying a diene elastomer requiring a control of the distribution of the species within the modified elastomer are essentially carried out in batch mode. Only the batch process makes it possible to refine the content of each species. Yet such a process is not always productive and sufficiently competitive and economic for industrial production.